Dental caries (decayed tooth) is a progressive disease to hard tissues of teeth, which is caused by a cooperative function of multiple factors in oral cavity. It is a major common oral disease with features of high incidence and wide distribution. Dental caries, along with cancer and cardiovascular diseases, are called the three major diseases of human being by World Health Organization. As reported by a survey of national oral epidemiology, the incidence of dental caries for the residents in China is 50% and the incidence of dental caries for deciduous tooth is 80%. According to the statistical result from the survey, the total amount of decayed teeth is up to 2 billion in China, 90% of which have never been treated. As estimated by a recent survey in America, nearly 80% of children and 90% of adults have been bothered by dental caries. As the development of economy and continuous improvement of living conditions, the dietary structure of modern people has also been changed to a great extent to contain more fine, sticky, and soft food and be rich in sugar, which causes dental caries easily. Dental caries, which has become the most epidemical bacterial infection disease, threats people's oral health severely. The defects in tooth tissues has a negative impact on oral functions such as chewing, language, and etc., and on aesthetics as they happen to the front teeth.
Microbes (e.g. streptococcus mutans) can form plagues on the surface of tooth enamel in an oral cavity, and the plagues, by producing acid and etching and demineralizing tooth enamel repeatingly, cause damage to tooth enamel and further to dentin. Dental caries, depending on the decayed extent, can be divided into three phases clinically, including shallow, moderate, and deep caries. In the phase of shallow caries, decay is only limited to enamel, and causes no obvious cavity. In the phase of moderate caries, decay reaches the superficial layer of dentin, and causes obvious cavities. In the phase of deep caries, decay extends to the deep layer of dentin, and big and deep cavities or cavities with small openings but wider damages in the deep layer appear. Dental caries can cause irreversible damage to the tooth enamel/dentin and loss of tooth function, and can also cause diseases to dental pulp and periapical tissue of root canal. The purposes of caries treatment are to stop the pathologic process of dental caries, to prevent its continuous progression, and to restore the inherent shape and function of teeth. Up to now, with respect to the existed caries, clinicians still use the method comprising steps of destructively grinding and removing decayed tooth tissues (including enamel and/or dentin), and using oral repairing material (including resin, metal, or ceramic) for filling and repairing (shown in the following Figures). These methods are unable to restore the original structure of tooth tissue, and may even cause potential problems of resulting in secondary caries and harming the biomechanical performance of tooth.
The greater damage caused by progression of dental caries can be stopped by preventing caries from happening on the layer of tooth enamel and providing nondestructive treatment on the early stage of tooth enamel caries. Despite owning an ability of remineralization, a tooth can not repair itself from a substantial damage due to its specific structure. Thus, for the tooth substantially damaged, a filling therapy is the most widely used method and has a better effect. The shape and function of a tooth can be restored using filling therapies, inlays, or artificial crowns according to ranges and sizes of tooth defects. Up to now, with respect to the existed caries, even to slight caries, clinicians still use the method comprising the steps of destructively grinding and removing decayed tooth tissues (including enamel and/or dentin), preparing a cavity with a suitable shape, and using biologically inactive oral repairing material such as resin, dental metal such as silver amalgam, or ceramic material for filling and repairing. Although favorable effects of restoring the shape and function of tooth tissues can be achieved by this repairing method in a short term, there will be secondary caries or breaks and shedding of the inlay in a long term due to contraction and aging of the material. However, with respect to the early enamel caries which are not suitable for the preparation of a cavity, or to some caries which do not possess resistance and retention, it is not appropriate to use the above material for filling.
Fluorapatite was first found in tooth by Heneh et al. Fluorapatite has the same crystal structure as hydroxyapatite with only a replacement of OH by F—. As known, fluorine has an electronegativity value of 4, the highest in all elements. Therefore, the bond strength between F— and Ca in fluorapatite is far greater than the bond strength between OH— and Ca in hydroxyapatite, which is one of the main reasons for the stability of fluorapatite. Since a variation in composition leads to a variation in performance of such material, domestic and international biomaterial scientists pay great attention to and proceed an intensive study on this issue. Because group F is smaller than group OH, fluorapatite has more compact crystal structure and thus smaller lattice constant than hydroxyapatite. Due to the more compact structure, fluorapatite has a lower solubility. Because of the significant meaning of this feature in clinical applications, fluorapatite can be used as a replacement material for bone and tooth. When fluorapatite is used as a nondegradable replacement material for hard tissues with high-load bearing structures, especially when fluorapatite is used as a dental material, the micro-release of fluorine ion can stimulate the growing of bone, and can also resist against erosion of body fluid and saliva to the material so as to shorten the healing period for bone. All these indicate great advantages of the biomaterial of fluorapatite.